Source of alternating current



' B. w. KENDALL sbuncr: 0F LTERNATING CURRENT F1194 Aug. '7, 1,918.

Nov. 17, 1925 v //1 1/80 for Ear/"0n W Kenda/Z y Ly Patented Nov. 17, 1925.

UNITED STATES 1,561,933 PATENT OFFICE.

BURTON W. KENDALL, OF NEW YORK, N- Y., ASSIGNOR TO WESTERN ELECTRIC COM PANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

SOURCE OF ALTERNATING CURRENT.

Application filed August 7, 1918. Serial No. 248,713.

To all whom it may concern:

Be it known that I, BURTON W. KENDALL, a citizen of the United States, residing at New York, in the county of New York, State of New York, have invented certain new and useful Improvements in Sources of Alternating Current, of which the following is a full, clear, concise, and exact description.

This invention relates to sources of alternating current, and in particular to alter-- nating current generators'employing vacuum tube amplifiers in which alternating electromotive forces are set up by reaction of the'output energy of a vacuum tube amplifier or other electron discharge device upon its input circuit.

More particularly, this invention relates to oscillation tube generators having atuned circuit for determining the frequency of the oscillations generated.

An object of this invention is to provide an improved means for determining the frequencyof a vacuum tube oscillator.

Another object of this invention is to provide means for excluding unidirectional current from the frequency determining circuit of a vacuum tube oscillator.

A further object of the invention is to provide means for enabling the use of a magnetic core inductance in the frequency determining circuit of a low frequency vacuum tube oscillator.

Still other objects and advantages will appear from the following detailed description, taken in connection with the accompanying drawing, in which Fig. 1 is a 'diagram of one arrangement of circuits for an oscillator according to this invention; and Fig. 2 is a diagram of a modified form of oscillator supplying oscillations to a vacuum tube amplifier.

Referring to Fig. 1, an evacuated container 1 having a filamentary'cathode 2, a

( grid or impedance controlling element 3 and a plate or anode 4, is shown with a grid or input circuit including transformer secondary winding 5 connecting cathode 2 and grid 3. Connecting cathode 2 and anode 4 is a plate circuit including a choke coil 6,

having aclosed oscillation circuit in shunt thereto, a variable resistance element 7, and a source 8 of space current, the positive terminal of which is connected to anode 4. The closed oscillation circuit shunting coil 6 comprises two branches, one including a variable capacity 9 and the other including a capacity element 10 and transformer primary winding 11 having a magnetic core. Cathode 2 is heated by a source 12 of heatmg current which is in circuit with a variable regulating resistance 13. Coupled to primary winding 11 is an additional secondary winding 14: by means of which oscillations may be supplied to line or work circuit 15.

In the operation of the system source 8 acts to supply space current through an external circuit including resistance 7 and choke coil 6. Resistance 7 serves to enable control of the value of this current and also of the amplitude of the oscillating current, whereby the output energy of the oscillator may be varied to meet changed conditions in the load circuit or to compensate for variations due to changes in the frequency of the current generated. Resistance '13 determines the temperature of filament 2. Choke 4 coil 6 prevents any variation current superposed on the normal space current from taking this path. If the closed oscillation circuit 9, 10, '11. be disturbed electrically oscillations will be set up of approximately the natural frequency of the circuit. Without the amplifying device these would soon be damped out. By virtue of coil 5 these oscillations set up an alternating voltage across the input elements of the tube which is of the frequency of the oscillations and differs in phase from the current in coil 11 by 90 degrees. The operation of the tube may be looked upon as setting up a voltage in phase with that of the'input voltage in its output. circuit thus tending to send a current of the same frequency through the circuits 1011, and 9 in parallel. These circuits constitute an anti resonant' circuit and as is well known when the frequency of the voltage applied The operational characteristics of the tube being a function of the magnitude of the alternating current in it, the latter adjusts itself to meet this condition. In this manner oscillations are produced and oscillating currents may be supplied from the closed oscillation circuit by primary Winding 11 to secondary winding 14: in the load or work circuit.

The frequency of the oscillations generated is principally determined by the electrical constants of the closed oscillatory circuits 9, 10, 11, that is, by the natural frequency of this circuit. l/Vhen the oscillator is to be used to produce oscillations of audio frequency, as for example, 1000 cycles per second, the natural period of the oscillation circuit must be comparatively large and this necessitates the employment of inductance elements of inconveniently large size unless a magnetic core is used with the inductance. Since the inductance of magnetic core devices varies with the flux density of the core and may be limited by the degree of saturation attained, it is very desirable that all flux due to steady or unidirectional currents be eliminated. This result is secured according to this invetnion by providing a separate path for unidirectional currents and by excluding such unidirectional currents from the inductance of the oscillation circuit.

It will be obvious that by varying capacity 9, the natural frequency of the closed oscillation circuit may be varied and the frequency of the oscillations generated may be controlled.

Capacity element 10 serves not only as a portion of the oscillatory circuit but also to block space current from the oscillatory circuit winding 11. This permits winding 11 to be run at a lower temperature, and, to an extent, reduces its resistance. This makes the normal resistance of this winding independent of the undirectional current of the output circuit. It also makes the normal inductance of this winding independent of variations that may occur in the space current and thereby causes the frequency to be set by-the tuned elements independently of the current in the tube. As previously explained, the exclusion of space current from the inductance element prevents its magnetic core from being subjected to the magnetizing action thereof, the normal magnetization of the magnetic core is accordingly low and a large variation in its flux density is possible, thus permitting a greater amplitude of oscillation currents to be obtained without distortion.

Fig. 2 illustrates a modified form of oscillator and means for connecting it to an amplifier. An evacuated electron discharge device 16 includes a hot filament cathode 17, a grid or impedance controlling clement 18 and a plate or anode 19. The space current path of the output circuit may be traced from filament 17, through variable source 20 of space current and choke coil 21 to the anode 19. The path for variation or oscillation currents is by way of closed oscillation circuit 22 and capacity element 28 in series therewith. The oscillation circuit 22 includes transformer primary winding 24; and variable capacity element 25, which together determine the frequency of the oscillations generated as explained in the description of the closed oscillation circuit of Fig. 1. The winding 24 is illustrated without a magnetic core but if it is desired to produce low frequency oscillations such a core may obviously be provided in the manner illustrated in Fig. 1. The input .circuit of the oscillator connecting its cathode and grid elements comprises a secondary. winding 26 inductively related to primary winding 24, and a variable source 27. of elect-romotive force, for keeping the grid at the proper normal potential with respect to the cathode. A conductor 28 connects filament 17 in series with filament 29 of a vacuum tube amplifier 30, and the filament heating circuit is completed through source 31, of heating current, and a filamenttemperature regulating resistance 32. The input circuit of amplifier 30 may be traced from filaliient 29 by way of conductor 28, secondary winding 33 and variable source 3i, which is connected to grid 35 of the amplifier 30 and serves to maintain this grid at the proper normal potential with respect to cathode 29. l/Vinding 33 is inductively related to primary windin 2% by which alternating electromotive forces are impressed from the oscillator upon the input circuit of amplifier 30. The space current circuit of amplifier 30 may be traced from cathode 29, by way of conductor 28, source 20 and choke coil 36 to plate or anode 37. Choke coil 36=excludes from the space current path the amplified oscillation currents which are .forced to traverse a shunt circuit between the cathode and anode, including blocking condensers 38 and 39 and primary winding 40 inductively related to secondary winding 41 of a high frequency transformer, by means of which oscillating energy is supplied to work transmission circuit 42.

The operation of the system illustrated in Fig. 2 is substantially the same as that of the. system of Fig. 1 and hence need not be explained in detail. Variable capacity 25 enables the natural frequency of oscillation circuit 22 to be varied as desired. Blocking condenser 23 preferably of large capacity prevents any. flow of space current in the ele ments of the oscillatory circuit and corresponds in function to element 10 of the previously described system, except that it has no effect in determining the natural frefrequency of the oscillations generated.

quency of oscillation circuit 22. Sources 27 and 34 keep their respective grids at proper normal potential with respect to the associated cathodes and accordingly serve to fix the normal impedance of each tube. ,In the case of the oscillator, this enables the amplitude of the oscillations to be controlled, whlle in the case of the amplifier, it enables operation at any desired point on the characteristic curve between output current and input eleotromotive force.

The thermionic amplifier 30 is asymmetrically conducting and accordingly prevents changes in the load circuit from re-' acting upon the oscillator and changing the It will, of course, be understood that while two specific circuit arrangements have been illustrated and described in detail, various changes in the general arrangement and in th details of the circuits may be made by those skilled in the art and this invention is therefore not to belimited to the circuits disclosed but only by the scope of the-.ap-

v pended claims.

What is claimed'isz 1. An oscillator comprising an electron .discharge device having input and-output.

discharge device having input and output circuits, an antl-resonant circuit determining the frequency of the.oscill'ations generated, said anti-resonant circuit coupllng said input and output circuits, an inductance elementin ,said anti-resonant circuit having a core of magnet1c material, and means to exclude unidirectional magnetizing current from said inductance element.

3. An oscillator comprising an electron discharge device having input and output circuits coupled to each other, said output circuit having a space current path and an oscillation path including an anti-resonant circuit for determining the frequency of the l generated current in parallel with said space current path, and means to exclude space 5'5 current from said oscillation path.

4.;An oscillator comprising an electron discharge device having input and output iticircuits' coupled to each-other, on'eQof said circuits including an anti-resonant. oscillas 'co circuit having an inductance winding asso.-

tion circuit, -.to determine the frequencies of the oscillations generated, said anti-resonant discharge device having a cathode, an anode and an impedance controlling element, an input circuit connecting said cathode to said controlling element, an output circuit connecting said cathode to said anode, said input and output circuits being coupled to each other, said output circuit having a space current path and, in parallel thereto, an oscillation path including an anti-resonant circuit for determining the frequency of the generated current, the said oscillation path including means to exclude space current from the path- 6. An oscillator comprising an electron discharge device having input. and output circuits coupled to each other, .said output circuit having a space current path and in Q parallel thereto an oscillation path including an anti-resonant circuit for determining the frequency of the generated current, and means in said oscillation path to exclude space current therefrom.

7. An oscillator comprising. an evacuated container including a hot cathode, an anode, anda conducting element. an external circuit for unidirectional current connecting said cathode to said anode, an anti-resonant circuit for determining the frequency of the oscillations produced connecting two points in said external circuit, means for excluding unidirectional current from said tuned circuit, and an input circuit connecting, said cathode and conducting element and coupled inductively to said tuned circuit.

8. An oscillation generator comprising an electron discharge device having input and output, circuits, the ouput circuit having a space current path and an oscillating current path including an anti-resonant circuit connected in parallel to the space current path which is adapted to determine the 'frequency of the oscillations produced and a resistance included in a portion of said output circuit throughwhich both alternating and direct currents flow, means for coupling said input and output circuits, and means for varying the resistance to change the alternating current output energy when desired because of frequency adjustment.

9. An oscillation generator comprising an electron discharge device having input and 1 output circuits, said output circuit having an path and a portion common to both direct and'alternating current paths, an anti-resonant circi1it-adapted to determine the fre quency of the oscillations generated included alternating ourrent path, a; direct current in said alternating current path and connected in parallel to the direct current path, 5 an adjustable resistance included in said common portion, and meansfor "coupling saidciated with a magnetic core, and means exeluding unidirectional current from said in- In witness whereof, I'hereunto subscribe a 'ductance winding. 1 my name this 1st day of August. A. 1)., 1918.1

5. An oscillator comprising an electron anti-resonant circuit and said input circuit};

' BURTON w. KENDALL-5 

